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Which Angles Match

Part of the Angles section of Coddy's Geometry journey. Lesson 46 of 59.

A triangle on its side is still isosceles, and its base angles are still opposite the ticked sides. They need not be at the bottom of the page, and the base need not be horizontal. Find them from the marks, never from the position.

$A tilted isosceles triangle PQR with PQ and PR ticked; the angles at Q and R carry matching arcs$

In the figure, PQ and PR carry the ticks, so they meet at the apex P. The side without ticks is QR, and the base angles sit at its ends: at Q and at R. The arcs show the pair. A quick test: each base angle is opposite one ticked side. The angle at Q faces PR, and the angle at R faces PQ.

Challenge

Triangle ABC is drawn on its side, with two sides ticked. Tap both base angles, the two angles that must be equal, then press Check.

Try it yourself

$Find the right part on the figure$

Find the right part on the figure

All lessons in Angles

1Meet the Angle

Your First Angle Angles on a Line Degrees and the Full Turn Across the Crossing

4Vertical Angles

Two Lines Cross Vertical Angles Are Equal Solving with Verticals All Four Angles Recap: At the Crossing

7Parallels and Transversals

Parallel Lines Corresponding Angles Alternate Angles Co-interior Angles Which Rule Is It Recap: The Three Pairs

10Isosceles and Equilateral

Base Angles Are Equal Finding the ApexWhich Angles MatchEquilateral Angles Isosceles at Work Recap: Twin Corners

2Naming and Equations

Adding Adjacent Angles Write the Equation Recap: Along the Line

5Around a Point

Angles Around a Point The Missing Angle Equal Slices Four Angles, One Point Recap: The Full Turn

8Angle Chases

Verticals Meet Parallels Is There Enough?From Figure to Equation Both Angles Labeled Recap: Through the Strip

11The Exterior Angle

The Exterior Angle Using the Shortcut Two Roads, One Answer Exterior in the Wild Recap: Outside View

3Right Angles and Complements

The Square Mark Complementary Angles Perpendicular Lines Finding the Complement Equal Parts of a Corner Recap: The Right Corner

6The Angle Bisector

The Angle Bisector Bisected Expressions Bisecting a Straight Angle Recap: Split in Half

9Triangle Angle Sum

The 180 Rule Finding the Third Angle Two Unknown Angles Right Triangles Recap: The Budget

12Final Challenges

Final: The Angle Chase Final: Triangle Meets Line Final: The Full Round Final: Isosceles Chase Final: Master of Angles